(567c) Thermodynamic Modeling of Coal Gasification: A Universal Approach

Gasification of feedstocks offer a promising route towards clean energy. However the characteristics of feedstock exhibit significant variations in composition (Prins et al., 2007). This introduces strong uncertainties in the predictions of the gas compositions exiting the reactor. This is complicated by the different kinds of gasifiers which exist , entrained beds, moving beds and fluidized beds. In this paper a thermodynamic approach is used to predict the performance of a gasifier. This enables us to predict performance of the system purely on the basis of stoichiometry and minimization of Gibbs free energy without depending on reaction rates (Li et al., 2001).  The ultimate analysis of coal is used to represent different types of coal. Different gasifying agents are considered like oxygen, steam, carbon-dioxide and combinations thereof. The simulations were performed on ASPEN Plus using RGibbs reactor model to predict the quantity of gasifying agent(s) required for complete carbon conversion (at which the cold gas efficiency is maximum) and the corresponding temperature and composition of synthesis gas. The gasifier performance for different gasifying agents is represented in terms of ratios of elements present in the feed stock. The trends predicted are consistent with those in the literature. The results presented here can be used to get an estimate of the efficiency of the gasification process for any composition of fuel and any combination of gasifying agents. The results of this approach can be used as inputs for preliminary design of gasifiers for any feedstock-gasifying agent combination. We show that it is possible to determine the optimum combination of the feedstocks which should be fed to a gasifier to get the highest cold gas efficiency.